1. Field of the Invention
The present invention relates generally to fiber optic cable assemblies deployed in fiber to the premises applications, and more specifically, to fiber optic cable assemblies including at least one network access point and methods for securing the collection of fibers at the network access point to allow for translation of the fibers without rotation.
2. Technical Background
Fiber optic networks are being expanded to provide voice, video, data and other services to subscribers. As a result, different cable types are being used to span both the long and short transmission distances. For kilometer length distribution cables, for example, these cables typically include one or more network access points along the cable length at which pre-selected optical fibers are accessed and preterminated to provide a branch off of the distribution cable. These network access points or “NAPs” are also referred to as “mid-span access locations” or “tap points” where preterminated optical fibers are spliced or otherwise optically connected to tether or drop cables. The types of networks in which cable assemblies are being developed are often referred to as “FTTx” networks, where “FTT” stands for “Fiber-to-the” and “x” generically describes an end location, such as “H” for “home.”
Certain cables that carry collections of fibers (“cable fiber assemblies) such as in the form of ribbon stacks and helically stranded buffer tubes present unique challenges for accessing and tapping. Specifically, challenges in how the access is performed, how the fibers are terminated, how the remaining uncut optical fibers or ribbons are handled, and how the cable performs over time and under stress. There are also challenges in mid-span accessing the cable fibers therein.
One type of fiber optical cable is a ribbon cable such as the Standard Single-Tube Ribbon (SST-Ribbon™) cable available from Corning Cable Systems of Hickory, N.C. This particular cable is helically wound and the cable fiber assembly comprises identifiable 12-fiber or 24-fiber ribbons in a filled buffer tube. Dielectric or steel rods are placed about 180 degrees apart in the cable's jacket to provide the required tensile strength for armored and dielectric constructions, respectively. This cable exhibits excellent water-blocking performance and is jacketed with a polyethylene outer jacket, and armored versions of the cable include a copolymer-coated steel tape armoring.
Another type of ribbon cable currently available includes the SST-Ribbon™ Gel-Free Cable also available from Corning Cable Systems of Hickory, N.C. The cable fiber assembly includes a single buffer tube that contains a stack of up to eighteen 12-fiber ribbons wrapped within a water-swellable foam tape. This central buffer tube is surrounded by a second water-swellable tape. Dielectric or steel strength members are located 180 degrees apart under the cable jacket to provide tensile and anti-buckling strength. The cable sheath is jacketed with a black UV-resistant polyethylene sheath and armored versions of the cable include a copolymer-coated corrugated steel tape armor layer. This cable can provide, for example, about 216 fibers in a compact design that can fit within a 1.0 inch inner diameter or larger inner-duct. Coupling features ensure that the ribbon stack and cable act as one unit, providing long-term reliability in aerial, duct and direct-buried applications and minimizing ribbon movement in situations where cable vibration may occur.
Such cables are typically used as trunk cables that provide an end-to-end connection rather than for providing mid-span access. The formation of mid-span NAPs is problematic in that spooling of such cables creates both a translation and twisting (torsion) of the ribbon stack carried within the cable. This would cause fixed NAPs to translate and twist and thus damage the ribbon stack at the NAP.
What is desired is a fiber optic cable assembly having at least one NAP and wherein the distribution cable is of a type including a cable fiber assembly that includes, for example, stack of optical fiber ribbons, such as the cable types described above. A desirable fiber optic cable assembly would provide structure or material for handling both the uncut fibers in the cable fiber assembly (e.g., ribbon stack) as well as the preterminated cable fibers (e.g., fiber ribbons). Further, what is desired are methods of creating NAPs along a fiber optic cable that allows for translation but not rotation of the cable fiber assembly.